Early bilingualism acquired from home or community is generally considered to positively influence cognitive development. The purpose of the present study was to determine to what extent bilingualism acquired through a second-language immersion education has a similar effect. Participants included a total of 106 French-speaking eight-year-old children drawn from two language groups: 53 children enrolled in English immersion classes since the age of five years (the immersion group) and 53 children enrolled in monolingual French-speaking classes (the monolingual group). The two groups were matched for verbal and nonverbal intelligence and socioeconomic status (SES). They were administered a battery of tasks assessing attentional and executive skills. The immersion group's reaction times were significantly faster than those of the monolingual group on tasks assessing alerting, auditory selective attention, divided attention and mental flexibility, but not interference inhibition. These results show that, after only three years, a second-language immersion school experience also produces some of the cognitive benefits associated with early bilingualism.